Measure from the outer edge of the seal on the original transfer case tailhousing to the center of the differential yoke u-joint. This measurement will be the center to center u-joint measurement for the new drive shaft and should be between 19 and 21 long. CV drive shafts are specifically made for NP231 slip yoke eliminator kits. Shafts are made using quality Dana Spicer components. Slip spline is coated to prevent corrosion. drive shaft tube and universal joints include grease fittings and grade 8 attaching bolts are included for CV yoke. Slip spline is 1-3/8 outside diameter and 1-7/8 outside diameter. Don't settle for inferior drive shafts when performing your offroad upgrades. Please follow the measuring procedure to select the correct drive shaft for your vehicle. If your measurement differs from the ones listed, these drive shafts should not be used.